Variable inductance device



june fi8 1935. w. .1 POLYDOROFF 2,005,2@3

VARTABLE INDUCTANCE DEVICE Filed May 4. 1932 Patented June 18, 1935` PATENT OFFICE VARIABLE INDUCTANCE DEVICE Wladimir J. Polydoro,

Chicago, Ill., allignor to Johnson Laboratories, Inc., Chicago, lll., a cor- Pntion of Illinois Application May 4, 1932, Serial No. 609,159

10Claims.

The invention relates to variable inductance devices which are particularly adaptable for highfrequency work, wherein inductance variations are effectuated by the movements of comminuted and compressed magnetic cores, relatively to inductance coils, such for instance as described in my Patent No. 1,940,228, issued Dec. 19, 1933, and my Patent No. 1,982,689, issued Dec. 4, 1934.

In the embodiments disclosed in my previous applications both the coil vand the core members were of constant diameter. It is an 0bject of the present invention to provide an improved construction for such variable inductance devices in which the desired relation between displacement of the core and the inductance variation is favored by giving the core members and the coil a novel shape.

In my previous patents, above mentioned, the advantage of employing different magnetic densities was described, these different magnetic densities being distributed throughout the length of one or both parts of the core, namely, the inner plug and the shell, which two parts may either be made integral in one operation, or molded separately and then cemented together or otherwise united.

As the performance of one of the methods of producing a core having such different densities is dependent upon the shape of the mold in which the parts of the core are compressed, it is important to so design said mold that smaller crosssections of the core receive pressure transmitted through larger cross-sections thereof, so that the energy losses due to the friction between the core and the inner wall of the mold will result in a reduction of the pressure against the smaller sections of the molded core, whereby their densities and permeabilities will be less than the densities and permeabilities of said larger sections.

It is, therefore, very useful to so construct these molds that a considerable taper will be given to both the outer wall of the inner plug and the inner wall of the outer shell, as illustrated in the drawing, wherein both the inner plug and the outer shell are shown as having a very noticeable taper to accentuate the diiferent densities thereof.

The invention will be better understood if reference be made to the accompanying drawing, which illustrates one embodiment of the invention and wherein- Figure 1 is a side view of separated parts of the inductance device;

Figure 2 is a longitudinal sectional view showing said parts assembled; and

Figure 3 is a sectional view showing a detail o! the invention.

The core comprises an outer shell I and an inner plug 2, the inner wall 3 of the outer shell and the outer wall I oi' the inner plug being tapered, as shown, and the densities of these parts and, consequently, their permeabilities, being increased toward the thicker ends 1a, 2a, so that, at said thicker ends, the larger and more eifective cross-sectional areas of the core are rendered still more eiective by said densities. Conversely, the smaller ends 1b, 2b, in which the cross-sectional areas of the core are relatively small and ineffective, are rendered still less efiective by their low densities.

Preferably, the shell l and the plug 2 are made independently and united at 5 by cement, the plug 2 having an enlargement 6 which spaces said shell and said plug from each other to thereby form an annular cavity 1 into which an inductance coil 8, borne by an insulating form 9 having a helical groove i0 in which the windings of said inductance may rest, may be inserted. Both the coil and the core are provided with screw-threaded members by which they may be attached to any suitable mechanism for producing the relative motion.

Hitherto, as disclosed in the above-mentioned patents, the coil was made of cylindrical form, but to secure the full advantage of a tapered magnetic core, a. tapered coil should be used, the coil taper being such that, when the coil is moved into the annular slot of the core, its walls are parallel with and in very close proximity to the outer surface of the inner plug of the core.

The coil and the core constitute a variable inductance device which may be used in highfrequency circuits to effectuate the tuning by moving the core and the coil relatively to each other. When the coil is removed from the core, minimum inductance of the variometer is secured, and, when the coil is moved in all the way, maximum inductance is obtained.

In certain high-frequency cases, it is desirable that the variation of the inductance shall be accelerated with the movement of the coil or the core.

It can readily be seen that if the tapered variometer is adjusted for minimum inductance, and the coil is gradually moved in, a very small amount of the less dense iron will be initially introduced into the larger end of the coil. As the -coil moves inside oi the core, larger and more dense masses of the iron are caused to coincide with smaller and smaller windings of the tapered coil, thereby introducing successively larger and more effective masses of iron per linear displacement of the coil.

In the final movement, when the coil is closing the gap between its inner wall and the tapered center core, the variation of inductance rapidly increases. Thus, in such a combined tapered structure of both the coil and the core, the inductance variation is continually increased, so that by a suitable design of the degree oi' taper and variable magnetic density, a variation of inductance approximating the squarey of linear displacement may be obtained. For instance, if the original air.- inductance of the variometer is microhenries, the inductance increases to microhenries, i. e., to twice its original value, when the coil is moved half way in, and increases to 400 microhenries when the remaining hal! of travel of the coil is completed. In such case, the inductance variation changes as the square of its linear displacement.

Having thus described my invention, what I claim is:

1. A variable inductance device, including a tapered magnetic core gradually increasing in density toward its larger end, and a correspondingly-tapered inductance coil inductively related to said core.

2. A variable inductance device, including a magnetic core having an annular cavity that is provided with a tapered inner wall, and a tapered inductance coil adapted to enter vsaid cavity and conforming to the taper of said inner wall.

3. A variable inductance device including a tapered inductance coil and a correspondinglytapered magnetic core longitudinally movable relatively to said coil, said core being variably spaced radially from said coil during said movement, the degree of taper on said coil and core being such that a desired relation oi' linear displacement to inductance change is secured.

4. A variable inductance device including a tapered inductance coil and a correspondinglytapered magnetic core longitudinally movable relatively to said coil, said core being variably spaced radially from said coil during said movement, the taper of said inductance coil and said magnetic core being such that the inductance variation is substantially proportional to the square of the linear displacement of the core.

5. A variable inductance device including a tapered magnetic core and a correspondingly tapered inductance coil, said core being linearly movable into the neld or said coil, the degree of taper of said coil and core being such as to produce progressively increasing increments oi' inductance for equal displacements.

6. A variable inductance device including a tapered magnetic core and a `correspondingly tapered inductance coil, said core being linearly movable into the eld of said coil and being spaced from said coil during its movement, whereby maximum inductance variation is secured with minimum eil'ect upon the distributed capacity of said inductance coil.

7. A variable inductance device including a magnetic core and an inductance coil, said core having a tapered inner portion and a cylindrical outer portion, said portions forming an annular cavity and being magnetically united at one end, said coil having a single-layer winding on an insulating form tapered to correspond to the taper of the inner portion of said core. 8. A variable inductance device according to claim 7, in which the portions of the core have increasing magnetic density toward the end at which they are magnetically united.

9. A variable inductance device including a magnetic core and an inductance coil, said core having an inner portion of varying diameter and an outer shell portion, said portions forming an annular cavity and being magnetically united at one end, said coil being wound in a helical groove on the surface of an insulating form tapered to correspond to the taper of the inner portion of said core.

10. A variable inductance device according to claim 9, in which both the core and the coil form include means whereby they may be secured to a mechanism for producing relative linear motion between said coil and said core.

WLADIMIR J. POLYDOROFF. 

